1. Field of the Invention
This invention relates to the field of foundations for buildings and other structures. More particularly, this invention relates to a pile cap employed in a foundation repair procedure, such pile cap being aligned between a load and a leveling pile positioned in the soil beneath the load.
2. Description of the Prior Art
Many buildings and other types of structures have been built on foundations or slabs made of concrete poured on top of soil. Constant changes in the weather and moisture levels in the soil frequently cause damage to such a foundation. In many instances, the foundation may buckle or even crack. This phenomenon occurs because prior to placing the foundation on the ground, the moisture beneath it is constant. Placing a foundation on the soil distorts the evaporation of the moisture underneath the foundation, thereby causing water build-up and relative soil swelling in the middle of the structure. Eventually, an uplifting can occur in the center because the moisture from around the edges relative to the center is drawn away by evaporation and/or by wicking action of the adjacent shrubbery. Over a period of time the foundation can "dome", causing its damage or failure.
There are several methods used in repairing foundations, some more effective than others. One of the most effective and widely used methods includes the use of one or more piles submerged into the soil beneath the foundation to form one or more supports. For clarity, the words "pile" and "piling" are synonymous terms signifying a single structure and the words "piles" and "pilings" are synonymous terms signifying a plural structure of more than one pile.
In such a procedure, there are several ways to construct and position a pile. Regardless of the manner in which a pile is constructed, however, most are made primarily of concrete and have an overall cylindrical shape with a length varying according to the soil type and weight of the structure. Most are positioned such that the top of the pile is within a relatively short distance from the bottom of the foundation.
Once the pile is positioned, the force of the building or other supported structure must be distributed on to the pile. Generally, the pile diameter is small relative to the downward force of the foundation; therefore, a means for gradually distributing the weight onto the pile is necessary. One way existing in the prior art to provide for such distribution is the use of a pile cap system consisting of different sized concrete blocks. The blocks are arranged to form an upside down or inverse stair-stepped frustum, with the block plane of the smallest surface area being placed on top of the pile. The other blocks are graduated in size upward from the top of the block on the pile to the foundation.
Several problems exist with the pile cap system just described. First, the blocks are heavy, cumbersome, and
PATENT difficult to maneuver. The positioning of the blocks relative to each other, the pile, and the foundation is critical; therefore, the maneuverability of the blocks is important. Once the blocks are in place, one or more power jacks or some other lifting means is positioned between the top concrete block and the foundation. These jacks are then used to lift the foundation to the necessary level, at which point they are replaced with additional permanent blocks.
The reason their positioning is critical is because of the unequal distribution of forces onto the pile cap system that create a rotational moment which, in turn, inherently makes the system unstable. A second problem associated with such a pile cap system is the destructive effect the shear stress has on the corners of the blocks that respectively overhang the corners of the blocks beneath them. Such stress can result in corner shearing and even without shearing reduces the strength of the blocks.
It is therefore a feature of this invention to provide an improved pile cap that is of lighter weight and is more maneuverable than those existing in the prior art.
It is also a feature of this invention to provide an improved pile cap that has an inherent resistance to the angular moment produced by the unequal distribution of forces onto the pile beneath the pile cap.
It is still a further feature of this invention to provide an improved pile cap that has a structure to minimize the destructive effects of shear stress on a pile cap.